Two memory
locations are important for custom characters on the Commodore Plus/4
and 16. Bit 2 of location 65298 controls whether character data is
fetched from ROM or RAM. The POKE in line 20 switches from the normal
ROM character definitions to a custom character set in RAM. The upper
six bits of location 65299 tell the computer where the character set is
located in memory. When POKEing to location 65299 it is important not
to disturb its lower two bits. To determine the number to POKE into
this location, divide the starting address of the custom character set
by 256. Since the example program puts the character set at location
15360, we use the POKE in line 30. The program uses a
machine language routine to copy the character set from ROM to RAM
beginning at location 15360. To copy the character set to some location
other than 15360, replace the second number in line 50 (currently 60)
with the number you POKEd into line 30. Line 40 reads the custom
character data from line 80 and POKES it into the area reserved for the
definition of the @ symbol.